Signal actuated control circuit



Jan. 21, 1964 c, us 3,119,027

SIGNAL ACTUATED CONTROL CIRCUIT Filed April 1, 1960 Claude [VLFausf IN V EN TOR.

BY @2245 @M geni" United States Patent 3,119,027 SIGNAL ACTUATED CONTROL CIRCUIT Claude M. Faust, Portland, Greg, assignor to Code-A- Phone Electronics, Inc, Seattle, Wash, a corporation of Washington Filed Apr. 1, 1960, Ser. No. 19,314

12 Claims. (Cl. 307-885) This invention pertains to electric control circuits and relates particularly to a control circuit in which the control of an electric load is dependent upon predetermined characteristics of an electrical input signal.

It is a principal object of the present invention to provide a control circuit by which an electric load is maintained activated by intermittent electrical input signals and is deactivated when the time between such intermittent signals exceeds a predetermined maximum.

Another important object of this invention is the provision of a control circuit by which an electric load is maintained activated by intermittent electrical input signals and is deactivated after a predetermined period of time following the introduction of a steady electrical input signal.

Still another important object of the present invention is the provision of a control circuit of the class described in which means is provided for varying the aforesaid predetermined periods of time.

Still another important object of this invention is the provision of a signal actuated control circuit which is characterized by the absence of mechanical relays.

A further specific objective of the present invention is to provide a voice actuated control circuit for use in telephone answering and recording apparatus, which circuit functions to maintain the apparatus activated by intermittent electrical input signals derived from speech received by the apparatus from a calling party, wherein the apparatus is deactivated either when a silent period following speech exceeds a predetermined maximum, or after a predetermined time following the initiation of the dial tone in a telephone line.

A still further object of the present invention is to provide a signal actuated control circuit which is of simplified construction for economical manufacture and provides long and faithful operation with a minimum of maintenance.

The foregoing and other objects and advantages of this invention will appear from the following detailed description, taken in connection with the accompanying drawing in which the single figure is a schematic diagram of a signal actuated control circuit embodying the features of this invention.

In the preferred circuit arrangement illustrated in the drawing, one side of the capacitor is connected through the resistance 12 to a terminal 14 of a source of negative potential. The opposite side of the capacitor is connected through the series arrangement of the diode rectifier 16 and potentiometer 18 to the base of the transistor 20. The emitter of this transistor is connected to a common ground or other source of potential which is positive with respect to the negative potential supplied at the terminal 14. The resistance 22 interconnects the base and the emitter to provide cut-off biasing for the transistor.

A second capacitor 24 is connected at one end between the rectifier 16 and potentiometer 18 and at the opposite 3,119,027 Patented Jan. 21, 1964 ice end to the ground or positive potential, to charge with the first mentioned capacitor 10.

The charging path of the capacitor 10 is shunted by the transistor 26 whose collector is connected between the capacitor 10 and resistance 12 and whose emitter is connected to the common ground or positive potential. The base and emitter of the transistor 26 are interconnected by the cut-off biasing resistance 28. As described more fully hereinafter, this transistor circuit provides a discharge path for the capacitor 10 through the diode rectifier 30 which is connected at its input side to the common ground or positive potential and at its output side between the capacitor 10 and the input of the first mentioned diode rectifier 16. The arrangement of this second rectifier functions to divert the charging path for the capacitor 10 through the transistor 20, and the arrangement of the first mentioned rectifier 16 functions to divert the discharge of the second mentioned capacitor 24 through the transistor 20.

The base of the transistor 26 is connected through the filter capacitor 32 and resistance 34 to the output side of a diode rectifier 36, the input side of which is connected to an output terminal 38 of a source of electrical input signals. The other output terminal 40 is connected to the common ground or positive potential.

The control circuit described hereinbefore functions to control the activation of an electric load of any desired type. For example, the load may be an indicator lamp or alarm, a recording instrument, a motor control, a capacitor in the circuit of another control transistor, and many others. In the specific embodiment illustrated in the drawing, the load is a relay coil 42 connected at one end to the collector of the transistor 20 and at the other end to the terminal 14 of the negative potential supply. The switch contacts 44, 46 associated with the relay coil are arranged in an electric circuit, the terminals 48, 50 of which may be connected to a device to be controlled, such as the telephone answering and recording apparatus mentioned hereinbefore.

The operation of the control circuit disclosed hereinbefore now will be described with reference to a telephone answering and recording apparatus. The input terminals 38, 40 are connected to the output of a telephone receiver amplifier and the terminals 48, 50 are connected to the electric circuit of the telephone answering and recording apparatus. Let it now be assumed that the telephone line circuit has been completed by an incoming call and the apparatus has informed the calling party that the apparatus will record a message which he may wish to give to the called party. The terminal 14 then is connected, as by means of a switch controlled by the apparatus, to the source of negative potential. Negative current thus is passed through the resistor 12, capacitor 10, rectifier 16, potentiometer 13 and base-emitter circuit of the transistor 20, to the common ground or positive potential. The capacitors 10 and 24 thus begin to charge, resulting in current flow in the base-emitter and emittercollector circuits of the transistor 20. The emitter-collector circuit thus functions as a switch in the circuit of the relay coil 42, the switch being actuated by current How in the base-emitter circuit. The relay coil 42 thus is activated, closing the associated switch contacts in the circuit of the apparatus.

The time required to fully charge the capacitor 10 is determined by the setting of the potentiometer 18, and this may be varied over a considerable range to provide the charge time desired. As an illustration, a charging time of about 15 seconds has been found to be desirable for the illustrated purpose.

When the capacitor 10 has been fully charged, current ceases to flow in the charging circuit. The charged capacitor 24 thereupon discharges through the potentiometer and base-emitter circuit to maintain the transistor 20 activated for a short period of time, for example about three seconds, for purposes explained more fully hereinafter. When the capacitor 24 becomes completely discharged, the transistor 20 is cut off and the relay coil 42 is deactivated, opening the circuit of the apparatus.

However, before capacitor 24 has completely discharged, let it be assumed that a calling party has begun to speak his message.

As the calling party speaks his message, the resulting alternating current signal to the input terminal 38 is rectified at rectifier 36 and passed through the filter circuit to the base of the transistor 26. Upon activation of this transistor its resistance is lowered, permitting the capacitor 10 to discharge through the collector-emitter circuit. Thus, the collector-emitter circuit of transistor 26 functions as a switch in the discharge circuit of capacitor 10, the switch being actuated by current fiow in the base-emitter circuit.

The capacitor 10 discharges during the intervals of speech signals, and since its discharge path does not include transistor 20 current ceases to flow through it from capacitor 10. However, during these intervals the capac itor 24 discharges through the transistor 20 to maintain the latter activated and the relay energized. A short discharge time of about three seconds for this capacitor has been found to be quite suitable for normal speech characteristics.

In the event of an interruption in speech signals for a period exceeding a predetermined time, for example about fifteen seconds, deactivation of the transistor 26 for that period of time will have caused the capacitor 10 to become fully charged, whereupon the transistor 20 will be deactivated and the relay coil 42 deenergized. This condition might arise, for example, when the calling party has completed his message but has failed to hang up the receiver within the fifteen second intervals.

In the event the calling party has finished his message and then hangs up the receiver, the dial tone on the telephone line causes the transistor 26 to be activated, whereupon the capacitor 10 discharges through it. Since the capacitor cannot recharge while the transistor 26 is activated, current will not flow in the base-emitter circuit of the transistor 20, after the second capacitor 24 has discharged through it, and hence the relay coil 42 will be deenergized.

Thus, with the control circuit of the present invention, an electric load such as the relay coil 42 is maintained energized as long as there is impressed upon the base of transistor 26 an intermittent electrical signal derived from an intermittent alternating current signal applied to input terminal 38. This alternating current signal may be provided by the telephone message described hereinbefore, or from'a radio signal or otherhigh frequency source. The electric load is deactivated when the intermittent signal is replaced either by a steady signal or by no signal, for a period of time determined by the setting of the potentiometer 18 which determines the charge time for the capacitor 10. The setting of the potentiometer also determines the discharge time for the capacitor 24, and this normally is chosen to be compatible with the time duration of the intermittent signal.

It will be apparent to those skilled in the art that various changes may be made in the values and arrangement of components described hereinbefore, without departing from the spirit of this invention and the scope of the appended claims.

Having now described my invention and the manner to secure by Letters Patent is:

1. A signal actuated control circuit for an electric load circuit, comprising a capacitance, a charging circuit for the capacitance, first switch means adapted for connection in the load circuit, first electrical switch actuator means including rectifier means for the first switch means connected in series with the capacitance in the said charging circuit for actuating the first switch means during charging of the capacitance, second switch means including an electric circuit releasably shunting the capacitance for discharging the latter, and second electrical switch actuator means for the second switch means and having an electric circuit, the second switch actuator means being operable by an electric signal to actuate the second switch means and shunt and discharge the capacitance, whereby to deactivate the first switch actuator means during discharge of the capacitance.

2. The circuit of claim 1 wherein the first switch means comprises the collector-emitter circuit or" a first transistor, the first switch actuator means comprises the base-emitter circuit of the first transistor, the second switch means comprises the collector-emitter circuit of a second tran sistor, and the second switch actuator means comprises the base-emitter circuit of the second transistor.

3. The circuit of claim 1 including means in the charging circuit for varying the charging time for the capacitance.

4. A signal actuated control circuit for an electric load circuit, comprising a capacitance, a charging circuit for the capacitance, first switch means adapted for connection in the load circuit, first electrical switch actuator means including rectifier means for the first switch means connected in series with the capacitance in said charging circuit for actuating the first switch means during charging of the capacitance, second switch means including an electric circuit releasably shunting the capacitance for discharging the latter, second electrical switch'actuator means for the second switch means and having an electric circuit, the second switch actuator means being operable by an electric signal to actuate the second switch means and shunt and discharge the capacitance, and a second capacitance shunting the first switch actuator means and connected to the said charging circuit for charging with the first named capacitance, the second capacitance functioning to discharge following full charge or during discharge of the first named capacitance, whereby to maintain the first switch actuator means activated for the additional time of discharge of the second capacitance.

5. The circuit of claim 4 wherein the first switch means comprises the collector-emitter circuit of a first transistor, the first switch actuator means comprises the base-emitter circuit of the first transistor, the second switch means comprises the collector-emitter circuit of a second transistor, and the second switch actuator means comprises the base-emitter circuit of the second transistor.

6. The circuit of claim 4 including means in the charging circuit for varying the charging and discharging time for the capacitances.

7. The circuit of claim 4 wherein the second switch actuator means is adapted for connection to a source of intermittent electrical audio signals.

8. The circuit of claim 4 wherein the second switch actuator means is adapted for connection to a telephone line circuit.

9. A signal actuated control circuit for an electric load circuit, comprising a capacitance, a charging circuit for the capacitance, a first transistor, the collector-emitter circuit of the first transistor being adapted for connection in the load circuit, the base-emitter circuit of the first transistor being connected in series with the capacitance in the said charging circuit, a second transistor, the collector-emitter circuit of the second transistor being connected across the capacitance, the base of the second transistor being adapted for connection to a source of electric signals for activating the second transistor, a second capacitance shunting the base-emitter circuit of the first transistor, and rectifier means in the charging circuit arranged to divert the discharge of the second capacitance through the base-emitter circuit of the first transistor.

10. The circuit of claim 9 including means in the charging circuit for varying the charging and discharging time for the capacitances.

11. The circuit of claim 9 wherein the base of the second transistor is adapted for connection to a telephone line circuit.

12. The circuit of claim 9 including rectifier means in the collector-emitter circuit of the second transistor.

References Cited in the file of this patent UNITED STATES PATENTS 2,606,251 Oberman Aug. 5, 1952 2,617,024 Hart Nov. 4, 1952 2,653,233 Carter Sept. 22, 1953 2,845,548 Sillrnan et al July 29, 1958 2,902,658 Erdrnan Sept. 1, 1959 2,998,532 Smeltzer Aug. 29,1961 

9. A SIGNAL ACTUATED CONTROL CIRCUIT FOR AN ELECTRIC LOAD CIRCUIT, COMPRISING A CAPACITANCE, A CHARGING CIRCUIT FOR THE CAPACITANCE, A FIRST TRANSISTOR, THE COLLECTOR-EMITTER CIRCUIT OF THE FIRST TRANSISTOR BEING ADAPTED FOR CONNECTION IN THE LOAD CIRCUIT, THE BASE-EMITTER CIRCUIT OF THE FIRST TRANSISTOR BEING CONNECTED IN SERIES WITH THE CAPACITANCE IN THE SAID CHARGING CIRCUIT, A SECOND TRANSISTOR, THE COLLECTOR-EMITTER CIRCUIT OF THE SECOND TRANSISTOR BEING CONNECTED ACROSS THE CAPACITANCE, THE BASE OF THE SECOND TRANSISTOR BEING ADAPTED FOR CONNECTION TO A SOURCE OF ELECTRIC SIGNALS FOR ACTIVATING THE SECOND TRANSISTOR, A SECOND CAPACITANCE SHUNTING THE BASE-EMITTER CIRCUIT OF THE FIRST TRANSISTOR, AND RECTIFIER MEANS IN THE CHARGING CIRCUIT ARRANGED TO DIVERT THE DISCHARGE OF THE SECOND CAPACITANCE THROUGH THE BASE-EMITTER CIRCUIT OF THE FIRST TRANSISTOR. 